Wrong return value in @spec for Graph.in_edges().

Hello. As I understand from the documentation, `Graph.in_edges()` is supposed to return "a list of `Graph.Edge`". However, the [`@spec`](https://github.com/bitwalker/libgraph/blob/main/lib/graph.ex#L2122C3-L2122C40) declares that only one edge is returned.
```elixir
@spec in_edges(t, vertex) :: Edge.t()
```

This is causing Dialyzer some discomfort:
```
Line 1193 Column 9: The pattern [Edge] can never match the type #{'__struct__':='Elixir.Graph.Edge', 'label':=_, 'v1':=_, 'v2':=_, 'weight':=number()}
Line 1194 Column 9: The pattern [Edge | More] can never match the type #{'__struct__':='Elixir.Graph.Edge', 'label':=_, 'v1':=_, 'v2':=_, 'weight':=number()}
```

Note that I'm using libgraph from an Erlang module, but of course, that shouldn't matter. I'm using version 0.16.0 of the library.